Cobalt base alloy and articles thereof



latentecl iViay UNITED STATES PATENT OFFICE 2,551,170 COBALT BASE ALLO AND ARTiCLIiS THEREOF Robert A. Schmucker, Jr., East Orange, Charles D. Preusch, Orange, and Lloyd F. Bowne, J12;

East Orange, N. J;, assignors to Crucible Steel Company of America, New York, N. Y., a corporation of New Jersey No Drawing. Application September 30, 1947, Serial- N0. 777,106

4 Claims. (01. 75-171) This invention pertains to cobalt-base, cast alloys containing carbon, chromium and metal of the group tungsten and molybdenum as essential constitutents, and such as are primarily adapted for cutting tools, particularly of the high speed variety, and which are also adapted for other wearand abrasion-resisting applications, for example dies.

For a number of years past, cast alloy cutting tools consisting basically of the above-mentioned elements have been used for machining at greater speed than is possible with high speed steels. In order to secure even greater cutting properties, other elements, such as boron, vanadium, tantalum and columbium, have been added to the basic cobalt-chromium-carbon-tungsten and/r molybdenum cast alloys aforesaid. Cutting tools containing one or more of these additional elements are now widely used commercially. v

The two principal requirements of a cobaltbase, cast alloy cutting tool of this type are:

that it must have sufficient wear or cratering resistance at elevated temperatures, to accomplish cutting at high speeds for a maximum length of time; and (2) it must have sufficient toughness to resist, under unfavorable conditions, chipping of the cutting edge or breaking of the tool bit itself. Carbon, boron, tungsten and chromium are among those elements which, while contributing to wear-resistance or general cutting life of the tool, can not be present in excessive percentages without producing an alloy which is too brittle.

In order to obtain a cobalt-base, cast cutting alloy having av composition. possessing the above required characteristics, most of the commercial cast cutting alloys of the type under consideration have been of analyses such as to fall within, or nearly within, the following percentage limits as regards the basic constituents, viz.:

C Cr W Co B -metal of the group tungsten and molybdenum within a restricted range of about 14 to 20% and preferably 16 to 19%, and boron in excess of 0.5, i. e., about 0.6 to 1.5% and preferably about 0.7 to 1%. In so far as we are aware, cobalt-base, cast cutting alloys within this range of analysis have never heretofore been produced commercially, or known to those skilled in the art, nor have the superior cutting qualities thereof been heretofore pointed out or suggested.

A.though either tungsten or molybdenum or both may be employed within the limits set forth in the above range of analysis for the present invention, tungsten is ordinarily preferred. Also, within these limits, the tungsten content should be decreased as the chromium content is increased, or vice versa, in order to avoid undue brittleness in the resulting-alloy.

The carbon content of alloys in accordance with the invention should lie Within the range of about 1' to 3%, and preferably about 1.5 to 2.5%. Carbon contents above about 2% generally produce heats with better results in log turning tests than do lower carbon heats. Boron contents over about 0.6% increase this tendency;

The qualities of alloys in accordance with the invention, when employed as cutting tools, are further improved by additions of other elements as follows:

Vanadium improves the toughness and the cutting properties of the alloy, and to this end should be present within broad limits of about 1.5 to 6%, and narrower limits of about 3 to 5%, vanadium of over 4% being preferred.

Nickel increases the toughness and decreases .the hardness of the alloy, and hence may be added for this purpose in amounts up to about 10%, and. more preferably up to about 6%, excellent results being obtainable with about 3% nickel. These same remarks-apply to iron, which may be added within these same'broad, preferred and recommended percentages.

Additions of nitrogen to the alloy in excess of about 0.1% and up to about 0.25% increase the cutting life of the alloy, and hence is a useful constituent of preferred analyses in accordance with the present invention. To this end, nitrogen may advantageously be added within the range of about 0.1 to 0.25% by weight of the resulting alloy.

Molybdenum, tungsten and chromium, in that order, are the most potent-hardeners of the a'ITOY and it is for this reason that increases in chromiuin within the range of the present invention must be accompanied by corresponding reductions in the amounts of molybdenum and tungsten, or vice versa. On the other hand, nitrogen, boron, carbon and vanadium appear to have By way of demonstrating the superiority of cast cobalt-base cutting alloys in accordance with the present invention, as compared to previously known and used alloys of this type, comparative cutting test results thereon are submitted in the following Table I. These cutting tests, the results of which are given in Table I, were for groups I-III carried out on an annealed chromium-nickel round log, approximating 15" in diameter, at a speed of 135 surface feet per minute, using a feed of 0.045" per revolution and a cutting depth of 1%". The cutting tests in group IV of Table I were carried out on a similar log of somewhat higher hardness at a speed of 110 surface feet per minute, using a feed of 0.040"

per revolution and a cutting depth of 1%".

Table I red by the present invention.

Although manganese and silicon appear to 5 have no particular advantageous or deleterious efiects on the alloy, when present in small amounts, they are ordinarily unavoidably present to some extent, but should be held within limits of about 1.5% each maximum, and the manganese should preferably be limited to about 0.5% and the silicon to about 1 Aside from the required and optional additions to the alloy above outlined, the balance thereof will be substantially cobalt.

A broad range of analysis for cobalt-base, cast only a slight effect on hardness within the range of analysis cove Nickel and iron, partially replacing cobalt, decrease hardness in that order.

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3. A cast cutting alloy having substantially the following composition: 35.5 to chromium; 14 to 20% of metal of the group tungsten and molybdenum, the metal of said group being substantially inversely proportional to the chro mium content; 1 to 3% carbon; 0.6 to 1.5% boron; 1.5 to 6% vanadium; upto 10% each of iron and nickel; up to 1.5% each of manganese and silicon; 0.10 to 0.25% nitrogen; and the balance cobalt.

4. A cast cutting alloy having substantially the following composition: 35.5 to 38% chromium; 16 to 19% of metal of the group tungsten and molybdenum, the metal of said group being substantially inversely proportional to the chromium content; 1.5 to 2.5% carbon; 0.? to 1% boron; 3 to 5% vanadium; up to 6% each of iron and nickel; up to 0.5% manganese; up to Table II Chemical Analysis, Per Cent (r'luttilg me 0 Tool Type Failure,

0 B (Jr W V Fe Ni Co (minutes) Commercial Alloy 1.4 0. 29.0 17.9 3.80 3.0 0.20 36.0 12.8 (AV.)

2. 0 0. 32. 0 20. 4 4. 50 Max. 3. 50 38. 0

Test tlfleats Representing the In- 1.9 0.75 35.5 16.0 3.75 3.0 3.00 Remainder 16.4 (Am) ven 1011.

2. 3 0. 37. 0 l7. 5 4. 25 Max. 3. 50

Test Conditions-Speed /130 SFM; Feed 0.045/Rev.; Depth of Cut 5%; Log: Annealed Chromium- Nickel Steel The improved cutting properties of cast cobalt-base cutting alloys in accordance with the present invention are thus clearly demonstrated by the results set forth in the above Tables I and II.

We claim:

A cast cutting alloy having substantially the following composition: 35.5 to 40% chromium; 14 to 20% of metal of the group tungsten and molybdenum, the metal of said group being substantially inversely proportional to the chromium content; 1 to 3% carbon; 0.6 to 1.5% boron; 1.5 to 6% vanadium; up to 10% each of iron and nickel; up to 1.5% each of manganese and silicon; and the balance cobalt.

2. A cast cutting alloy having substantially the following composition: 35.5 to 38% chromium; 16 to 19% of metal of the group tungsten and molybdenum, the metal of said group being substantially inversely proportional to the chromium content; 1.5 to 2.5% carbon; 0.? to 1% boron; 3 to 5% vanadium; up to 6% each ofiron 1% silicon; 0.1 to 0.25% nitrogen; and the balance cobalt.

ROBERT A. SCHMUCKER, JR. CHARLES D. PREUSCH. LLOYD F. BOWNE, JR.

REFERENCES CITED The following references are of record in the a file of this patent:

OTHER REFERENCES Progress Report on Heat Resisting Metals for Gas Turbine Parts (N-102), P. B. No. 39,579; September 21, 1943, stamped: Declassified to open February 18, 1946; page 6. 

1. A CAST CUTTING ALLOY HAVING SUBSTANTIALLY THE FOLLOWING COMPOSITION: 35.5 TO 40% CHROMIUM; 14 TO 20% OF METAL OF THE GROUP TUNGSTEN AND MOLYBDENUM, THE METAL OF SAID GROUP BEING SUBSTANTIALLY INVERSLY PROPORTIONAL TO THE CHROMIUM CONTENT; 1 TO 3% CARBON; 0.6 TO 1.5% BORON; 1.5 TO 6% VANADIUM; UP TO 10% EACH OF IRON AND NICKEL; UP TO 1.5% EACH OF MANGANESE AND SILICON; AND THE BALANCE COBALT. 